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Although the role of intense psychological distress in psychopathology has been recognized for centuries, the metaphorical use of the word 'trauma' to indicate intense psychological distress only became popular in the midst of the industrial revolution (Danese & Baldwin, 2017). The introduction of the steam engine and the spread of railways led to a sharp increase in train accidents. Strikingly, many accidents involved previously healthy individuals who developed mental illness even in the absence of physical injury - the socalled 'railway spine'. These unusual observations triggered a heated debate. On the one side, there were proponents of organic explanations (e.g. Oppenheim), who thought train accidents could have caused yet undetectable brain injuries leading to psychopathology. On the other side, there were proponents of functional explanations (e.g. Charcot), who thought that the mental/intrapsychic representation of the accidents - socalled 'psychological' trauma - could lead to psychopathology.
Neurobiological research is reconciling this conflict by suggesting that psychological trauma, and particularly childhood psychological trauma, can trigger the same physiological response as physical trauma. The biological plausibility of this theory is supported by experimental and observational studies showing that psychological stress can trigger an immune response or, more precisely, an inflammatory response (Steptoe, Hamer, & Chida, 2007), presumably with the aim of preparing the body to face potential physical injury (Segerstrom & Miller, 2004). Psychological stress can induce activation of the amygdala and consequently of the sympathetic nervous system, which in turn triggers activation of immune cells and the inflammatory response (Bierhaus et al., 2003). Inhibitory systems, namely the hypothalamic-pituitary-adrenal (HPA) axis and the parasympathetic nervous system, generally keep the inflammatory response at bay preventing its chronic activation.
Psychological traumas occurring early in life may, however, have long-term effects on the immune system. Of note, individuals with a history of childhood trauma, such as childhood maltreatment, show greater amygdala reactivity to emotional stimuli (van Harmelen et al., 2013) and, thus, may more often experience activation of the inflammatory response. Furthermore, they show reduced HPA axis signalling (Heim, Newport, Mletzko, Miller, & Nemeroff, 2008), and, because of the impairment in this inhibitory pathway, they may also show chronic elevation in inflammation levels. We reported initial evidence of association between childhood maltreatment and high levels of several inflammation biomarkers in 1000...